The invention relates generally to rotary die apparatus for creasing or scoring cardboard or paperboard material used in the manufacture of cartons, boxes, point of purchase displays and the like and relates more specifically to an improved scoring rule for such rotary die apparatus.
Cutting dies for shaping and forming sheet material such as corrugated board can be flat or rotary. Rotary dies are used for their higher production rates. Such apparatus includes counter-rotating, horizontally disposed die and anvil cylinders mounted to a frame with a gap of predetermined thickness between them. Both the die and anvil cylinders are typically metal. The die cylinder carries a die board mounted thereon, with the appropriate cutting and scoring rules. A resilient urethane sleeve covers the anvil cylinder. As the corrugated blank is drawn between the cylinders, the cutting die, in cooperation with the anvil cylinder, cuts a blank from the sheet material and forms score-lines where the blank is to be folded.
The shape of the blank is laid out on a plywood die board including cuts, perforations, and fold lines. Saw or laser cuts are used to form slits which receive the cutting rules.
Some cutting die configurations require female dies on the anvil cylinder to align with the corresponding male dies on the die cylinder. Alignment is critical to quality and the die sets are costly to produce. This art is the subject of significant patent activity. U.S. Pat. No. 3,884,132 teaches a magnetic rule to align the female dies before affixing them to the anvil plate with pressure sensitive adhesive. U.S. Pat. No. 3,919,924 discloses a mechanical locator strip to align the female die. As preparation and alignment of the female die is costly, additional art provides for the elimination of the female die. U.S. Pat. No. 4,373,929 teaches separate cutting and scoring dies.
Cracking of the paperboard can be a significant problem. U.S. Pat. No. 5,221,249 addresses this issue by providing a rigid, undulating rule.
Variation in die board thickness led to the development of two different fields of art, cylinder contact rules and surface mount rules. U.S. Pat. No. 3,673,929 shows a scoring rule with metal flanges that project through slots in the die board and contact the metal die cylinder. Resilient scoring rules use the traditional surface mount method but flex in operation to compensate for die board variation. U.S. Pat. No. 4,289,492 discloses a scoring rule of plastic material having a longitudinally-extending ridge centrally located on the topside to form the score. U.S. Pat. No. 5,194,064 provides a complex set of creasing elements spaced laterally to produce a discontinuous score lines.
Finally, both U.S. Pat. Nos. 5,582,571 and 5,641,551 add teeth to the rule to create a controlled perforation to weaken the paperboard for folding.